1. Field of the Invention
The present invention relates to an ultrasonic sensor in which an ultrasonic detecting element is attached to an acoustic matching member.
2. Description of Related Art
There is conventionally known an ultrasonic sensor in which an ultrasonic detecting element is attached to a substrate made of a metal, a resin material or the like. The ultrasonic sensor transmits an ultrasonic wave by using an element capable of transmitting the ultrasonic wave, and receives the ultrasonic wave, which collides with and is reflected from a detected body by using an element capable of receiving an ultrasonic wave, thereby performing a position measurement or a distance measurement of an object in the surroundings, or a measurement of a two-dimensional configuration or a three-dimensional configuration of the object.
Such an ultrasonic sensor may be provided with an acoustic matching layer, which adjusts acoustic impedance to improve a transmission efficiency of transmitted/received ultrasonic waves. For example, there is known an ultrasonic sensor in which an acoustic matching layer is fixed on one face of an ultrasonic detecting element composed of a piezoelectric element, the acoustic matching layer being formed to have a thickness of one fourth of the ultrasonic wave by a material, in which glass balloons are diffused in an synthetic resin (refer to JP-10-224895A).
Here, in a case of mounting the above type of ultrasonic sensor in a vehicle such as an automobile for use, an acoustic matching layer in the ultrasonic sensor is fixed by a material such as a metal. Therefore, ultrasonic waves are transmitted via the acoustic matching layer from this material to an ultrasonic detecting element thereof, and thereby this may create the cause of noises. Further, the material restrains oscillation of the acoustic matching layer caused by the ultrasonic wave to damp the oscillation, leading to reduction in detection sensitivity to the ultrasonic wave.